1. Field of the Invention
The invention relates to a nuclear power plant with a water or liquid sodium coolant and a metallic component having surfaces coming into contact with the coolant.
2. Description of the Prior Art
While, due to special development work, the metallic materials used for the construction of nuclear power plants, primarily austenitic steels, are more corrosion-resistant and can be activated (for instance, by giving up cobalt content) less strongly or only for shorter periods of time as compared to the materials used in conventional technology, nevertheless it has been found that components of the metallic materials which come into contact with coolant do go into solution in the coolant even if only to a very small extent. In addition to the changes caused thereby, mostly detrimental to the original metallurgical properties, this leads in the area of the reactor cooling loop to an extensive deposit of radioactive materials in the overall loop, which limits its accessibility for servicing and repair. This may involve materials activated at their original location or materials which are activated only in the dissolved state when passing through the fission zone of the nuclear reactor.
Experts have heretofore attempted to counter these detrimental effects by the choice of particularly corrosion-resistant materials or by coating the surfaces subjected to the coolant. For nuclear power plants operated with liquid sodium as the coolant, it has been proposed, for instance, to make the components wetted thereby of a vanadium alloy. This, however, leads to the desired result only if a high degree of purity of the sodium coolant can be assured which necessitates considerable effort for its regular purification. Molybdenum has been used as the coating material, for instance, for the cladding tubes of nuclear fuel rods. However, due to diffusion effects between the coating and the base material (particularly at high temperatures), pores develop in time at the boundary surface between the base material and the coating, whereby the coating is damaged.
In order to facilitate the decontamination work usually required in servicing and repair work due to these effects, one strives from the start to make the surfaces concerned therewith very smooth. This necessitates increased manufacturing costs for the surface treatment.